Communication devices such as wireless communication devices, that simply may be named wireless devices, may also be known as e.g. User Equipments (UEs), mobile terminals, wireless terminals and/or Mobile Stations (MS). A wireless device is enabled to communicate wirelessly in a wireless communication network that typically is a cellular communications network, which may also be referred to as a wireless communication system, or radio communication system, sometimes also referred to as a cellular radio system, cellular network or cellular communication system. A wireless communication network may sometimes simply be referred to as a network and abbreviated NW. The communication may be performed e.g., between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more Core Networks (CN), comprised within the wireless communication network. The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, just to mention some further examples. Wireless devices may be so called Machine to Machine (M2M) devices or Machine Type Communication (MTC) devices, i.e. a device that is not necessarily associated with a conventional user, such as a human, directly using the device. MTC devices may be as defined by 3GPP:
The wireless device may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communication network covers a geographical area which is divided into cell areas, wherein each cell area is served by at least one base station, or Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is typically identified by one or more cell identities. The base station at a base station site provides radio coverage for one or more cells. A cell is thus associated with a geographical area where radio coverage for that cell is provided by the base station at the base station site. Cells may overlap so that several cells cover the same geographical area. By the base station providing or serving a cell is meant that the base station provides radio coverage such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station in said cell. When a wireless device is said to be served in or by a cell this implies that the wireless device is served by the base station providing radio coverage for the cell. One base station may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g., a Radio Network Controller (RNC) in Universal Mobile Telecommunication System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g., in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communication (originally: Groupe Spécial Mobile).
UMTS is a third generation mobile communication system, which may be referred to as 3rd generation or 3G, and which evolved from the GSM, and provides improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices.
General Packet Radio Service (GPRS) is a packet oriented mobile data service on the 2G cellular communication system's global system for mobile communications (GSM).
Enhanced Data rates for GSM Evolution (EDGE) also known as Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC), or Enhanced Data rates for Global Evolution is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM.
High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Such networks may be named WCDMA/HSPA.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks. LTE may be referred to as 4th generation or 4G.
The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
Work is ongoing with developing a next generation wide area networks, which may be referred to as NeXt generation (NX), New Radio (NR), or fifth generation (5G). A design principle under consideration for 5G wireless communication networks is to base it on an ultra-lean design. This implies that “always on” or frequent signals, may need to be avoided in the network as much as possible. The expected benefit from this design principle is expected to be significantly lower network energy consumption, better scalability, higher degree of forward compatibility, lower interference from system overhead signals and consequently higher throughput in low load scenario, and also improved support for user centric beam-forming.
Advanced Antenna Systems (AAS) is an area where technology has advanced significantly in recent years and where a rapid technology development in the years to come is also foreseen. Hence, it may be natural to assume that advanced antenna systems in general and massive Multiple Input Multiple Output (MIMO) transmission and reception in particular, will be a cornerstone in a future 5G wireless communication network.
As beam-forming becomes increasingly popular and capable, it becomes natural to use it not only for transmission of data but also for transmission of control information. This is one motivation behind the relatively new control channel in LTE known as enhanced Physical Downlink Control CHannel (ePDCCH). When a control channel is beam-formed, the cost of transmitting the overhead control information may be reduced due to the increased link budget provided by additional antenna gain. This is a good property that may likely be utilized also for 5G, perhaps to an even larger degree than what is possible in the currently in LTE.
In many wireless communications systems CSI (Channel-State Information) feedback may be considered crucial for obtaining good performance. Reference signals may be transmitted which may be used to estimate the channel state, whereupon the reported CSI feedback may typically include a CQI (Channel-Quality Indicator) and RI (Rank Indicator) value. More detailed reports may include frequency-selective CQI and/or PMI (Pre-coding Matrix Indicator) values.
The 3GPP LTE (Long Term Evolution) system supports CSI-reporting schemes that rely on the reference symbols being transmitted periodically; the cell-specific reference symbols (CRS) may be sent every subframe, while the user-specific CSI-RS may be sent with a larger periodicity. UEs using transmission mode 10 (TM10) may rely solely on CSI-RS resources, while other UEs typically use the CRS at least for interference measurements. Furthermore, UEs using TM10 may be configured with multiple CSI processes, each estimating and reporting CSI of a specific channel and interference situation, while other transmission modes may only support a single CSI process.
When a UE is in active mode it may be all the time prepared to, in an optimized way, receive and transmit data from/to the network, which means that a UE in active mode is configured with one or more CSI processes and CSI are continuously reported to the network. However, when the UE is in idle mode the UE, to save battery life-time, typically passively monitors RSRP (Reference Signal Received Power) of CRSs of cells it may be able to detect. As long as the UE moves in an area within the current tracking area, the area served by cells that may reach/page the UE, the UE does not communicate with the network. Only if the UE approaches an area outside its current tracking area it may need to initiate communication with the network and go to active state in order to perform a tracking-area-update. In the tracking-area update, the UE needs to communicate with the core network and therefore it initiates communication with the eNB in order to be able to transmit and receive data. The UE will be configured to one or more CSI processes that will be used by network to efficiently transmit data, e.g. proper selection of rank, modulation and coding, and pre-coder.
In NR, it is planned to include an alternative/additional state, which may be named a dormant state where the UE may still be configured but not active, e.g., as when connected and able to transmit and receive data, e.g., user data. This state may be described as somewhere in between the legacy, i.e., conventional idle and active modes/state.
In 5G, network nodes are expected to support many antenna elements that enable beamforming transmitted energy towards the UE. This has the advantage of improving radio coverage of the UE. However, the signalling overhead expected to be involved for a UE to report the radio conditions to the network is significant due to the increased number of beams the UE may need to measure and report back to the network.